Somatosensory evoked potential monitoring in carotid surgery. II. Comparison between qualitative and quantitative scoring systems

Abstract

This paper compares the respective yields of our SEP scoring system ('qualitative' criteria), based on the subdivision of SEP abnormalities into mild, moderate, and severe abnormalities, and a quantitative one ('classical' criteria), based on a more than 1 ms CCT increase or 50% decrease of N20 amplitude, for the detection of brain ischemia justifying shunt placement during carotid endarterectomy (CE). For that purpose, we examine the sensitivities of several neurophysiological parameters (the ipsilateral and contralateral CCT, the amplitudes of the ipsilateral and contralateral frontal and parietal SEPs) to carotid cross-clamping or to a drop of blood pressure. Our data first confirm that shunted patients developed a CCT increase and a decrease of N20 amplitude on the ipsilateral hemisphere. They further demonstrate that 50% of the patients who were immediately shunted on the basis of qualitative criteria would not have been shunted or would have been shunted with a longer delay on the basis of quantitative criteria. Simultaneously, the overall percentage of shunted patients was not significantly higher than in studies using the 'classical' criteria. Thus, it was hard to decide between the 'qualitative' and the 'classical' criteria on the basis of patient data. However, our 'qualitative' system appears advantageous in that it smooths out the influence of factors liable to interfere with the quantitative parameters.